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Tcl/Tk 8.5 Programming Cookbook

Tcl/Tk 8.5 Programming Cookbook

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Tcl/Tk 8.5 Programming Cookbook

Tcl/Tk 8.5 Programming Cookbook

3 (7)

Overview of this book

With Tcl/Tk, you can create full-featured cross-platform applications in a simple and easy-to-understand way without any expensive development package; the only tools required are a simple text editor and your imagination. This practical cookbook will help you to efficiently interact with editors, debuggers, and shell type interactive programs using Tcl/Tk 8. This cookbook will comprehensively guide you through practical implementation of Tcl/Tk 8.5 commands and tools. This book will take you through all the steps needed to become a productive programmer in Tcl/Tk 8. Right from guiding you through the basics to creating a stand-alone application, it provides complete explanation of all the steps along with handy tips and tricks. The book begins with an introduction to the Tcl shell, syntax, variables, and programming best practices in the language. It then explores procedures and the flow of events with control constructs followed by advanced error trapping and recovery. From Chapter 4, a detailed study of string expressions and handling enables you to handle various string functions and use lists to expand the string functionality. The book then discusses in-depth the Tcl Dictionary and how to utilize it to store and retrieve data. File operations and Tk GUI handling are covered extensively along with a developing a real-world address book application to practice the concepts learned.
Table of Contents (20 chapters)
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Tcl/Tk 8.5 Programming Cookbook
Credits
About the Author
Acknowledgment
About the Reviewers
www.PacktPub.com
Preface

Using the error command


The primary usage of the error command is to programmatically raise an error. This allows you to interrupt the interpreter at the desired point and to present the user with an error message of your choice.

Getting ready

To complete the following example, we will need to create a Tcl script file in your working directory. Open the text editor of your choice and follow the given instructions.

How to do it…

In the following example, to illustrate, we will generate an error and a supporting error message in a location where it should not occur. Using the editor of your choice, create a text file named error.tcl that contains the following commands:

if {1+1==2} {
error "My Error"
}

After you have created the file, invoke the script with the following command line:

% tclsh85 error.tcl
My Error
while executing
"error "My Error""
invoked from within
"if {1+1==2} {
error "My Error"
}"
(file "error.tcl" line 1)
child process exited abnormally
%

How it works…

As you can see, in the...

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